Materials for growing algae and artificial fishing banks

ABSTRACT

Vitreous, algae growing materials, release stably ferrous ions, over long periods of time. The duration of ion release can be controlled as desired by adjusting the particle size of the materials. The vitreous, algae growing, materials can be converted into porous forms or fabricated into at least parts of structures. The vitreous, algae growing, materials consist essentially of 15 to 50 weight percent SiO 2 , 1 to 35 weight percent either or both of Na 2 O and K 2 O, 30 to 70 weight percent B 2 O 3 , and 1 to 40 weight prercent of either or both of FeO and Fe 2 O 3 . Increasing the content of boron facilitates the release of ferrous ions from the vitreous, algae growing, materials.

FIELD OF THE INVENTION

This invention relates to materials for promoting marine plant andphytoplankton propagation that are placed on the surface of the sea orat depths where sunlight reaches, or in rearing facilities on landcomprising borosilicate glass, containing boron and iron. This inventionalso relates to artificial reefs to rear fish and shellfish by promotingmarine plant and phytoplankton propagation, at least a part of which iscovered or built with the aforementioned borosilicate glass.

BACKGROUND OF THE INVENTION

Various types of steel, rock and concrete armor blocks have been placedon the bottom of the sea, either as they are or as assembled artificialreefs; to grow seaweed and other marine plant necessary to providefeeding and living grounds for fish and shellfish. Also, variouscontrivances have been used with these structures, to form appropriatelyrugged surfaces on them.

However, their functions are limited to providing substrata for seaweedand other marine plants to put their roots down on.

Seaweed and other marine plants including phytoplankton grow on variousdissolved nutrients in seawater, including, nitrogen, phosphorus,silicon, manganese and iron. Particularly ferrous ions of iron dissolvedin seawater are said to make significant contributions to their growth.

With this growth promoting effect in mind, the inventors proposed, asper Japanese Provisional Patent Publication No. 335330 of 1994 (JapanesePatent No. 2577319), algae rearing materials, consisting of vitreousmaterials, containing ferrous ions embedded therein that releas; whensunk into the sea, ferrous ions, stably, over long periods of time. Thealgae rearing materials, just mentioned comprise, by weight, 30 to 70percent silicon dioxide, 10 to 50 percent sodium oxide and/or potassiumoxide, 5-50 percent iron oxide, plus manganese oxide and phosphoruspentoxide as required, and containing not less than 1 percent ferrousions. They are, for example, coated on to the surface of appropriatestructures which are sunk into the sea. They promote the growth ofseaweeds and other marine plants by providing suitable rearing sites forlong periods of time by continuously releasing minute traces of ionsinto the surrounding seawater.

Recently, however, the vitreous materials are required to release moreferrous ions with a smaller glass supplies to fulfill the followingneeds:

1) To vitalize the entirety of seaweed beds with very small quantitiesof growth promoting materials.

2) To promote the growth of diatoms that become the initial feed in therearing of abalone and sea-urchin by using smaller quantities of growthpromoting materials releasing ferrous ions.

3) To promote growth of phytoplankton in offshore areas where planktonis difficult to grow because of the shortage of iron, by spraying smallquantities of growth promoting materials over wide areas.

Conventional growth promoting materials, when added in large quantitiesto seawater in water tanks, or other closed systems, have a tendency toraise the pH of the seawater through the release of potassium, sodiumand other alkalis. Acid additions are required to avoid this rise in pH.Therefore, growth promoting materials causing less pH increase arerequired.

Meanwhile, global warming caused by rising levels of atmospheric carbondioxide presents a significant problem. Strategies on global warmingthat will lead to upsetting of ecosystem balances, and the rising of sealevels are being studied on a global scale.

One of possible solutions attracting attention is the growing of marinealgae. While seaweed and seagrass grow on the bottom of relativelyshallow coastal sea not deeper than 20 m, phytoplankton is distributedin large areas of sea all over the world to depths where sunlightpenetrates. It is known that these marine plants annually absorbapproximately 30 billion tons of carbon from seawater and convert itinto organic matter. If, as such, the number and species of marineplants, especially phytoplankton that make up the greater part thereof,are increased, they will absorb and fix more carbon dioxide fromseawater. If the carbon dioxide in seawater decreases, the sea will makeup for the loss by taking in an equivalent amount of carbon dioxide fromthe atmosphere because of the equilibrium relationship between theatmosphere and the sea, thereby decreasing the amount of carbon dioxidein the atmosphere.

Based on this already known relationship, preliminary experimentationhas already been carried out in the growing of phytoplankton by sprayingsolutions of ferrous ions over sea surface areas containing sufficientamounts of nitrogen, phosphorus, silicon and other elements needed byphytoplankton but lacking iron required for their growth. Suchexperimentation has proved that solutions of ferrous ions spread overthe surface of the sea are effective for growing phytoplankton (seeMartin et al. (1994); Testing the Iron Hypothesis in Ecosystems of theEquatorial Pacific Ocean, NATURE, vol. 378(8), Sept. pp. 123-129).

Although their effectiveness has been thus confirmed, spreadingsolutions of ferrous ions requires large quantities of water andenormous costs for transportation. Besides, it is difficult to maintainthe effect of ferrous ions for long periods of time because theirsolutions readily diffuse from the area in which they are sprayed. Thisproblem may be solved by supplying iron compounds that release ferrousions at and near the surface of the sea. However, ordinary ironcompounds and metallic iron cannot provide a long-lasting phytoplanktongrowing effect because they quickly sink from the surface to the bottomby virtue of their high specific gravities. Also, ordinary ironcompounds and metallic iron are unsuitable for practical use as theycannot continue the stable release of ferrous ions over long periods oftime.

While some vitreous materials, releasing ferrous ions of have beenalready proposed as mentioned earlier, it is desired to use suchvitreous materials that release ferrous ions more efficiently withsmaller glass supplies.

Now, an object of this invention is to provide algae growing materialsconsisting of vitreous materials, having greater capabilities to releaseferrous ions.

Another object of this invention is to provide artificial reefs or otherforms of seaweed beds prepared by shaping said algae growing materials,into various shapes or incorporating them in various substratastructures, that are to be placed in artificial rearing sites orfacilities or in natural sea areas.

Algae, especially phytoplankton, grow by photosynthesis while floatingor drifting at or near the surface of the sea or at depths havingadequate light penetration. Ferrous ions promote the photosynthesis ofphytoplankton. Therefore, it is necessary to continue a stable supply offerrous ions to depths with adequate light penetration, preferably todepths of a few meters. Thus, still another object of this invention isto provide porous, algae growing materials capable of a long-lastingstable supply of ferrous ions, in sea areas where phytoplankton isdistributed and consisting of vitreous materials releasing ferrous ionsand having lower specific gravities than seawater.

SUMMARY OF THE INVENTION

This invention achieves the above objects by the following:

(1) An algae growing material consisting of a vitreous material capableof releasing ferrous ions into water and consisting essentially of, byweight, 15 to 50 percent SiO₂, 1 to 35 percent either or both of Na₂Oand K₂O, 30 to 70 percent B₂O₃, and 1 to 30 percent either or both ofFeO and Fe₂O₃.

(2) An artificial reef for growing algae consisting of a reef structureconsisting of, at least in part, or covered with a vitreous materialcapable of releasing ferrous ions into water and consisting essentiallyof, by weight, 15 to 50 percent SiO₂, 1 to 35 percent either or both ofNa₂O and K₂O, 30 to 70 percent B₂O₃, and 1 to 30 percent either or bothof FeO and Fe₂O₃.

(3) A porous, algae growing material consisting of a porous, vitreousmaterial having independent foamed pores, containing 1 to 40 percenteither or both of FeO and Fe₂O₃ and capable of releasing ferrous ionsinto water.

(4) A porous, algae growing material consisting of a foamed vitreousmaterial described in (3) above containing, in addition to theconstituent described in (3), 15 to 50 percent SiO₂, 1 to 35 percenteither or both of Na₂O and K₂O, 30 to 70 percent B₂O₃.

This invention takes advantage of the amorphousness of vitreousmaterials. Amatrix of an amorphous vitreous material, carrying iron,embedded therein, is capable of continuing a slow, stable andlong-lasting release of ferrous ions into seawater by the erosiveactions thereof. The large quantities of boron (30 to 70 percent asB₂O₃) added to vitreous materials accelerates the release rate of iron(ferrous ions) and makes a significant contribution to the growth ofalgae.

Vitreous materials form random network structure containing positiveions (network-former) such as silicon and boron combined with oxygenrandom network, positive ions (network-modifier) such as sodium andpotassium entrapped in the network structures, and iron ions serving asnetwork-former and network-modifier. When such a vitreous material isimmersed in seawater, the OH⁻ ions in water combine with the positiveions on the surface of the vitreous material and form NaOH and KOH whichbreak the bonds between silicon and boron. The vitreous materialgradually releases its constituents over a long period of time.

Generally, borosilicate glasses consisting essentially of boron (10 to25 percent as B₂O₃) and silicon (under 70 percent as SiO₂) are known tohave high chemical durability and heat resistance. This invention isbased on a new discovery that glasses whose chemical durability isdecreased by varying their boron content release large quantities offerrous ions. In addition, the release of boron ions inhibits the risingof the pH of the surrounding water resulting from the release of alkalis(potassium, sodium, etc.) generally contained in vitreous materials.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A more detailed description of this invention is given in the following.

Vitreous algae growing materials of this invention contain silicon,sodium and/or potassium, boron and iron, in combinations within thefollowing ranges, as the source for releasing ions.

Silicon, which is a basic component that forms an amorphous networkstructure, is contained within the range 15 to 50 weight percent asSiO₂. If the silicon content is under 15 percent, the network formingfunction of silicon becomes dependent on boron and the waterproofingquality of glass deteriorates. Even moisture in the atmosphere sometimesdissolves the network structure. If the silicon content exceeds 50percent, the network structure becomes stronger, the strength of theglass itself also increases (both chemically and structurally), and therelease of iron and other elements decreases.

Either or both sodium and potassium are contained, as Na₂O and K₂O,within the range 1 to 35 weight percent in total. Sodium and potassium,when added within said range, break the network structure of the glassand control the release rate of iron ions.

Iron, which is indispensable for the release of ferrous ions plays animportant role in the growth of algae, and is contained as either orboth FeO and Fe₂O₃ within the range 1 to 40 weight percent. Under 1percent, a sufficient release of ferrous ions is unobtainable. Whencontained in excess, on the other hand, iron precipitates as metalliciron, rather than entering the glass as iron ions. Then, uniformdispersion of iron is not attained in the glass. The metallic iron atthe surface might break the glass because they have differentcoefficients of thermal expansion. Therefore, the upper limit of ironcontent is set at 40 weight percent.

Boron is contained, as B₂O₃, within the range 30 to 70 weight percent.As stated earlier, the addition of 30 percent or more boron changes theproperty of the glass and promotes the release of ferrous ions. However,boron addition in excess of 70 percent deteriorates the waterproofingquality of the glass.

This invention also provides algae growing materials consisting ofporous, vitreous materials containing ions as FeO and/or Fe₂O₃ withinthe range 1 to 40 weight percent, and having a specific gravity of 0.1to 1.0 and a capability to continuously release ferrous ions. Theporous, vitreous materials having independent foamed pores and aspecific gravity of 0.1 to 1.0, preferably 0.2 to 0.5, will float ordrift on the surface of the sea or at depths permitting lightpenetration. The algae growing materials made of such materials can befastened to buoys or other similar structures placed on the surface orin the sea. The ferrous ions continuously supplied from such materialsover long periods of time are conducive to the growth of algae,especially phytoplankton. The constituents of the vitreous materials arewithin the ranges described earlier.

A vitreous, algae growing material of this invention is prepared bymixing appropriate quantities of known materials containing silicon,boron, iron, and sodium and/or potassium. The mixture is then vitrifiedby a known process consisting of fusing by heating at a high temperature(for example, at 1200 to 1500° C. for approximately 20 to 60 minutes)and subsequent cooling. In this vitrifying process, ferrous ion contentof the glass can be increased by carrying out fusion in a reducingatmosphere obtained by the use of coke or other reducing agent or carbonmonoxide or other reductive gas.

A porous, vitreous material of this invention is prepared either bypreparing a vitreous material containing a necessary quantity of ferrousions and fusing a mixture of the vitreous material thus prepared and afoaming material under heat or by simultaneously fusing a vitreousmaterial and a foaming material under heat.

For example, a porous, vitreous material is prepared by mixing 100 partsby weight of a powder of a vitreous material prepared as described above(preferably having an average particle size of 300 μm or under) with 1to 10 parts by weight (preferably 2 to 5 parts by weight) of a powder ofsilicon carbide or carbon and heating the mixture at 600 to 900° C. forapproximately 5 to 60 minutes using an electronic oven or other similardevice.

The same goal can be achieved by injecting air, nitrogen or othersimilar inert gas into a fused vitreous material (a process known as“bubbling”).

Porous, vitreous materials can be obtained by also bringing a fused,vitreous material into contact with such compounds as sodium phosphateand potassium phosphate that generate gas through thermal decompositionor by adding coke or other reducing agent that generate gas whencombined with oxygen to the starting materials and fusing the mixtureunder heat.

Although the shape and properties of the porous vitreous materialsaccording to this invention are not limited, it is preferable that theyhave spherical or an irregularly crushed shape 3 to 100 mm across(preferably 5 to 5 mm across).

The algae growing materials according to this invention are used invarious shapes, plates, sheets, powders, lumps, spherical, and crushedforms, either singly or in combination. Increasing the surface area bymaking the surface of the algae growing materials rough increases therelease rate of iron ions therefrom. As described in the following, thealgae growing materials of this invention are ideally suited to growingand increasing phytoplankton and algae in natural seas and also inartificial culture facilities.

For example, lumps or granules of the vitreous algae growing materialsof this invention put in bags may be placed in the water of culturetanks to grow sea urchin, abalone, turban shell and other shellfish.Then, the vitreous materials promote the growth of the young of seaurchin and shellfish by effectively increasing the numbers of diatoms(microscopic algae) that serve as their food.

Ferrous ions are indispensable for the mass culture of floating diatom;feeding bivalves and microalgae, feeding fish and shellfish inartificial rearing installations. Therefore, the vitreous algae growingmaterials of this invention stably releasing ferrous ions over longperiods of time are ideal. They are particularly ideal for thecontinuous mass culture of species of microalgae containing largequantities of β-carotene.

Also in the culture of seaweeds, especially the kelps known as Undaria(wakame) and Laminaria (kombu), which are sometimes tended in watertanks or other artificial systems until they have grown from sporophyteto young fronds. Granules of the vitreous algae growing materials ofthis invention placed in such water tanks will promote the growth oftheir spores to young fronds measuring approximately a few millimetersin size.

The vitreous algae growing materials are sometimes used in porous forms.

Ferrous ions are essential for the growth of phytoplankton. Some seaareas though, containing much nitrogen, phosphorus and silica ions, donot permit the multiplication of phytoplankton because of the shortageof iron. If a vitreous algae growing material, particularly a porousone, of this invention is added, such sea areas will become capable ofpermitting the multiplication of phytoplankton. Containing not only ironions but also silica ions, the vitreous algae growing materials of thisinvention are suited for the rearing of floating diatoms.

The vitreous algae growing materials of this invention can also be usedfor artificial reefs. The vitreous, algae growing materials may becoated or affixed, either singly or as a mixture with other materials,on part or the whole of other structures (of concrete, steel, stone,waste from construction sites, natural rock, etc.) or used on parts ofsuch structures.

The algae growing materials according to this invention, thus placed inthe sea, release stably ferrous iron and silica ions over long periodsof time, thereby contributing to the growth of algae, and aid in thegathering of fish and shellfish preying on such algae, and in the fixingof carbon dioxide.

It is said to be preferable that algae growing materials containphosphorus and manganese; 1 to 30 weight percent as P₂O₅ and 0.1 to 5weight percent as MnO. They also contain Al₂O₃ and some otherimpurities. This invention does not exclude the existence of thesecomponents.

EXAMPLE 1

100 parts of silica sand, 13.9 parts of soda ash, 36.1 parts ofpotassium carbonate, 28.7 parts of hematite, 11.5 parts of coke, and312.3 parts of boric acid, all by weight, were mixed in a mixer. Acrucible fed with the obtained mixture was put in an electric ovenpreheated to 1400° C. and allowed to melt for 30 minutes. By droppingthe molten product thus obtained on to a steel plate, an algae growingmaterial in glass-sheet form having the properties shown in Table 1 wasobtained.

Example for Comparison 1

A powder of hematite, silica sand, potassium phosphate and phosphoricacid was weighed so that the compositions shown in Table 1 would beobtained. Then, it was thoroughly mixed with coke and put in a crucible.The crucible was put in an oven preheated to 1400° C. in which areducing atmosphere was maintained by supplying town gas. Vitreousmaterials obtained by placing the mixtures under heat for 1 hour werethen cooled to room temperature. Table 1 shows molded vitreous materialsA, B and C (algae growing materials for comparison) thus obtained.

TABLE 1 Algae Chemical Compositions (In % by weight) growing Oth-materials FeO Fe₂O₃ SiO₂ Na₂O K₂O P₂O₅ B₂O₃ ers Example 1  6.7 1.7 29.7 2.4  7.3 — 52.2 0.02 Example A 11.8 2.9 37.5 — 39.3 8.4 — 0.03 for com-parison Example B  5.0 1.2 57.6 13.5 12.4 10.2  — 0.05 for com- parisonExample C 21.8 5.5 46.5 13.6  8.3 4.2 — 0.04 for com- parison

(1) Accelerated Ion Release Test

The algae growing material obtained as Example 1 and Examples A, B and Cfor comparison were crushed into particles 300 to 850 μm in diameter. 10grams each of the crushed samples were taken and boiled for 2 hours in100 ml of seawater heated to approximately 100° C. Then, the contents ofiron, silicon, sodium, potassium, phosphate, and boron in the boiledsolutions were determined, along with the pH thereof. The contents ofiron, manganese and silicon were determined by the method disclosed inJapanese Provisional Patent Publication No. 335330 of 1994. The contentsof boron and phosphorus were determined by spectroscopic analysis usinginductively coupled plasmas. The content of sodium and potassium wasdetermined by diluting the eluates obtained in the ion release test andapplying an atomic absorption analysis (the frame method) thereto.

Table 2 shows the results of analytical determination and the pH's ofthe individual boiled solutions. In Table 2, the value 0 is assigned tothe contents below the limit of detection.

TABLE 2 (In mg/100 ml) Amounts released Total iron SiO₂ Na₂O K₂O P₂O₅B₂O₃ pH Example 1 103.1 3.41 170 530 — 4110 6.2 Example for 0.06 0.03 —1940 384 — 11.65 comparison A Example for 0 5.7 200 160 0.84 — 8.9comparison B Example for 0.04 0 300 14.5 0.13 — 8.8 comparison C

As is evident from the results shown in Table 2, the algae growingmaterials consisting of the vitreous materials of this invention releasea remarkably large quantity of total iron while having a pH of 6.2representing a level of acidity very close to neutrality. That is, thealgae growing materials of this invention proved to release iron,including divalent iron, ions at high rates.

(2) Ion Release Test at Ordinary Temperature

The algae growing materials obtained in Example 1 and Example forComparison 1-B were crushed into particles between 300 and 850 μm indiameter. Approximately 0.2 g and 1 g of the granulated specimens weretaken from the materials prepared in Example 1 and Example forComparison 1-B, respectively. Each of the specimens was immersed in 200ml of seawater at 20° C. (with a pH of 8.0), continuously stirred with astirrer, and then allowed to stand. The release rate of iron in seawaterat ordinary temperature was investigated by determining the contents oftotal iron in each sample of seawater 10 minutes, 30 minutes, 45minutes, 1 hour, 2 hours and 3 hours after the start of allowing tostand and stirring. The results are shown in Table 3.

In this release test at ordinary temperature, the total iron content wasmeasured to determine the difference in the release rate between theconventional algae growing materials and those according to thisinvention.

TABLE 3 Algae Growing Weight of Total Iron Material Specimen (g) ReleaseRate (μg/g/hr) Example 1 (Not stirred) 0.2167 60.0  Example 1 (Stirred)0.2033 407.2  Example for comparison 0.9759 4.7 1-B (Not stirred)Example for comparison 1.1004 4.6 1-B (Stirred) (Note) Particle size:300 to 850 μm

As is obvious from Table 3, the release rate of total iron in seawaterat ordinary temperature differs significantly between the algae growingmaterial of this invention and the one prepared for the purpose ofcomparison.

EXAMPLES 2-5

An algae growing material consisting of vitreous material according tothis invention was prepared in the same manner as in Example 1, exceptthat the contents of fluttery silica sand, soda ash, potassium carbonateand hematite were varied as shown in Table 4.

TABLE 4 Algae growing Chemical Compositions (In % by weight) materialsFeO Fe₂O₃ SiO₂ Na₂O K₂O B₂O₃ Others Example 2 6.5 1.6 28.9 3.0 9.0 50.80.02 Example 3 6.6 1.6 33.5 3.1 9.1 46.1 0.03 Example 4 9.3 2.3 27.9 2.98.7 48.9 0.02 Example 5 6.6 1.7 29.4 6.0 4.8 51.6 0.02

An accelerated release test was conducted by the method describedearlier. Table 5 shows the results of an analytical determination andthe pH's of the individual boiled solutions. The content of boron wasnot determined as it was not considered an active ingredient of thealgae growing material.

TABLE 5 (In mg/100 ml) Amounts released Total iron SiO₂ Na₂O K₂O pHExample 2 30.9 3.6 200 520 6.3 Example 3  5.40 4.4 100 400 6.9 Example 448.8 3.8 200 470 6.6 Example 5 15.2 3.5 400 310 6.5

The results in Table 5 show that the algae growing material consistingof vitreous material of this invention exhibit significantly high totaliron release rates and pH in the range of 6.3 to 6.9 representing alevel of acidity very close to neutrality. That is, the algae growingmaterial according to this invention releases iron including ferrousions at high rates without raising the value of pH in the surroundingenvironment.

EXAMPLE 6 (1) Preparation of Porous Vitreous Material

100 parts by weight of the vitreous material prepared in Example 1 wascrushed. The crushed material was mixed with 1 to 5 percent by weight ofsilicon carbide. Then, porous vitreous materials were obtained byheating the obtained mixture at 710° C. for 15, 30 and 45 minutes. Theobtained porous vitreous materials had the same chemical composition asthe starting material, and obtained indicated specific gravities asshown in Table 6.

TABLE 6 Heat Treatment Percent Addition of Foaming Agent Time 1% 3% 5%15 minutes 0.51 0.40 0.30 30 minutes 0.40 0.28 0.25 45 minutes 0.36 0.220.20

In the specimen prepared by adding a 1 percent foaming agent with a heattreatment for 15 minutes, foamed pores were independent but small, under1 mm, in diameter, with a higher specific gravity. The specimen preparedby adding 5 percent foaming agent with a heat treatment for 45 minutes,foamed pores were larger, between 5 and 10 mm, and had somewhat lowerstructural strength. The number of foamed pores did not increase inproportion to the increase in the percentage of foaming agent addition.The percent addition between 1 and 5 percent was a practicallyappropriate range.

(2) Preparation of Specimens According to This Invention

The specimen prepared by adding a 3 percent foaming agent with a heattreatment for 30 minutes proved to have adequate buoyancy, withuniformly distributed foamed pores, 1 to 2 mm in size, adequatestructural strength, and a specific gravity as small as 0.28.

This porous vitreous material was crushed into a specimen with aparticle size of 2 to 7 mm (porous specimen 1) and a specimen with aparticle size of 7 to 13 mm (porous specimen 2). These two specimens hadindependent foamed pores of 1 to 2 mm in diameter.

(3) Preparation of Specimens for Comparison

The vitreous material prepared in Example 1 was crushed to a specimenwith a particle size of 2 to 7 mm (nonporous specimen 1) and a specimenwith a particle size of 7 to 13 mm (nonporous specimen 2).

(4) Divalent Iron Ion Release Test in Seawater

0.5 to 4 g of each specimen ware put in 200 liters of seawater at roomtemperature (approximately 20° C.) and allowed to stand for 15 minutesto 2 hours. Then, the concentration of ferrous ion in the seawater wasdetermined by the silica-gel column method using 8-hydroxyquinoline.Table 7 shows the values thus determined. In Table 7, the release ratesof ferrous iron ions (Fe²⁺) are the values converted for the addition of1 g of each specimen.

(5) Test Results

TABLE 7 Particle Immersion Release Rate Specimen Size Time of Fe²⁺Nonporous specimen 1  2-7 mm 2 hours 0.5 μg/g/hr Porous specimen 1  2-7mm 15 minutes 26 μg/g/hr Nonporous specimen 2 7-13 mm 2 hours 0.06μg/g/hr Porous specimen 2 7-13 mm 15 minutes 11 μg/g/hr

The porous vitreous materials according to this invention havingindependent foamed pores and lower specific gravities float and drift onthe sea surface. Having greater areas of contact with water, inaddition, the porous vitreous materials have greater ferrous ion releaserates than the nonporous vitreous materials of the same composition. Theporous specimens 1 and 2 have 52 times and 183 times respectively,greater release rates than the non-porous specimens 1 and 2.

Also, the release rate increases with decreasing particle size.Therefore, the required ferrous ion release rate and supply to thetarget sea area can be determined by adjusting the particle size.

To achieve effective growth of phytoplankton, individual sea areasrequire iron for different lengths of time. It is said that such periodsare three months for the Antarctic Ocean, twelve months for theequatorial region, and six months for the sub-Arctic regions. To savethe costs of transportation and spraying, it is necessary to adjust theduration of iron release. The duration of iron release can be controlledby adjusting the chemical composition, particle size of foamed pores ofthe porous vitreous materials according to this invention.

Industrial Applicability

As discussed above, the algae growing materials of this inventionpromote the growth of algae and multiplication of phytoplankton whenthey are placed on or near the sea surface or at depths with adequatelight penetration or in rearing facilities on land. The algae growingmaterials of this invention are particularly suited for the promotion ofthe multiplication of phytoplankton in cultivation. Also, they can beused as, for example, artificial reefs by coating them on otherstructures or by incorporating them in such structures. Furthermore,porous vitreous materials having lower specific gravities drift on thesea surface or at depths with light penetration while stably releasingferrous ions over long periods of time. Besides, the release time can becontrolled to the required period by adjusting the particle size.

The vitreous materials containing silicon are conducive to the growingof phytoplankton. Phytoplankton form the base of the food chain. Themultiplied phytoplanktons will feed living things of higher orders, thusincreasing the number of fishes and, as a consequence, the volume offishery production.

When phytoplankton increase, their photosynthesising fixes the carbondioxide in seawater, in algae, with some portions thereof sinking togreater depths, thereby fixing carbon in the depths of the sea. Somephytoplankton will feed living things of higher orders while someportions of such living things will become human food, thus promotingthe progress of favorite material cycles.

A shortage of carbon dioxide in the sea can be made up by taking in partof the carbon dioxide released into the atmosphere by the burning offossil fuels. The resulting reduction in carbon dioxide in theatmosphere will permit a reduction of global warming.

What is claimed is:
 1. An algae growing material consisting of avitreous material capable of releasing ferrous ions into water andconsisting essentially of 15 to 50 weight percent SiO₂, 1 to 35 weightpercent either or both of Na₂O and K₂O, 30 to 70 weight percent B₂O₃,and 1 to 40 weight percent either or both of FeO and Fe₂O₃.
 2. Anartificial reef for rearing algae, comprising or covered with, at leastin part, a vitreous material capable of releasing ferrous ions intowater consisting essentially of 15 to 50 weight percent SiO₂, 1 to 35weight percent either or both of Na₂O and K₂O, 30 to 70 weight percentB₂O₃, and 1 to 40 weight percent either or both of FeO and Fe₂O₃.
 3. Analgae growing material consisting of a porous vitreous material capableof releasing ferrous ions into water, containing 1 to 40 weight percenteither or both of FeO and Fe₂O₃, having independent foamed pores and aspecific gravity of 0.1 to 1.0.
 4. An algae growing material accordingto claim 3, wherein the vitreous material further contains 15 to 50weight percent SiO₂, 1 to 35 weight percent either or both of Na₂O andK₂O, 30 to 70 weight percent B₂O₃.